Electrical sound reproducing system



H. C. FORBES ELECTRICAL sounn REPRODUCING SYSTEM Original Filed March 2, 1955- I I I8 I n I I I I I l I I l I I I I l I I I I l I I l I 1NVENTOR. ME'NRY C. Fonsss ATTORNEY.

Patented Jan. 9, 1940 ELECTRICAL SOUND REPRODUCING .1 SYSTEM Henry C. Forbes, Buffalo, N. Y., assi'gnor to 0010- nial Radio Corporation, Buffalo, N. Y., a corporation of New York Application March 2, 1935, Serial No. 8,982 Renewed July 28, 1939 9 Claims.

This invention relates to electro-acous'tic'ap- 1 I paratus and more particularly to apparatus embodying an electrically operated loud speaker, actuated by currents derived from apparatus positioned at a point more or less remote from the loud speaker. The. invention is particularly useful in connction with automobile radio receivers, although it will be understood that the principles and apparatus herein disclosed are not limited to use therein, but may be utilized in other forms of apparatus for other purposes.

In general, my invention contemplates utilizing the conductors which lead the voice currents to the loud speaker for the purpose of performing.

other desired functions without interfering with their primary action in carrying VOiCe currents. In certain installations, and particularly in automobile radio installations, where the speaker is located at a distance from the radio receiver and connected thereto by wiring, the wiring is desired to be installed in a very limited internal space, and it may be desired to pull the wiring into position. without disturbing outer structural members.

This is particularly the case where it is desired to mount the loud speaker in the top of a car, or above the windshield, and the radio receiver chassis beneath the dash or behind the instrument panel. In such cases, in order to avoid unsightly exposed wiring, it is desired to run the wires up through the corner post of the car. in which the space is very limited. At the same time it may be desired to control the apparatus from a position at or adjacent the speaker.

This invention comprehends among its objects, to provide apparatus whereby the operation of the system may be controlled or modified in various ways, from a position at or near the loud speaker; utilizing for the purpose only the two conductors customarily used, and herein em ployed, for feeding sound currents to the speaker. Among the various operations which may be so controlled in accordance with my invention, I may enumerate, by way of example and without excluding others not specifically mentioned;

Controlling and adjusting the tone quality of the reproduced sounds;

Supplying the field excitation to a dynamic loud speaker;

Providing radio or audio frequency links between the speaker and the source of sound currents therefor; A

Controlling by relay certain desired functions of the source of sound currents. as for instance, turning the receiver on and off, shifting the reception band, etc.

Still other objects and advantages of my invention will be apparent from the specification. The features of novelty which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its fundamental principles and as to its particular embodiments, will best be understood by reference to the specification and accompanying drawing, in which Fig. 1 is a circuit diagram showing how the tone quality of the reproduced sounds may be controlled at or near the speaker without the necessity for providing additional conductors between the speaker and the source;

Fig. 2 is a similar diagram of such a system arranged to supply the field excitation for the speaker without providing additional conductors;

Fig. 3 is a similar diagram of such a system arranged to provide a radio or audio frequency link between the speaker and the source of sound currents without providing additional conductors, and

Fig. 4 is a similar diagram of such a system for operating a relay for performing desired functions at the source of sound currents under control from a position at or near the speaker without the necessity for additional conductors.

In the various figures, like reference numerals indicate like parts.

Referring now more particularly to Fig. l, I have shown diagrammatically a source of sound currents in the form of an output tube This may be the final audio frequency amplifying stage of a radio receiver of any desired construction. or of an electrical phonograph, an aud'o frequency amplifier with microphone input, and I am not concerned with the details of construction of such stage, which is well known in the art. It may be a single tube, as illustrated, or it may comprise a pair of tubes connected in push-pull, or a single twin tube affording pushpull operation within a single envelope.

By way of example I have illustrated a typical construction of such stage, the tube comprising a cathode 2. a heater 3 therefor, a control grid 4, and an anode 5. Connected in the anode-cathode circu't there is shown the primary of a suitable audio frequency transformer 6, and a source of plate potential 9. The negative side of the source of plate potential is indicated as connected to one sde of the heater and also to grounded conductor M. which isshown as connected to the cathode through resistance l5 shunted by condenser IS The primary of the audio frequency transformer supplies currents to the secondary], to the opposite terminals of which are connected the conductors II and I2, leading to the loud speaker. These conductors are connected to the opposite terminals of the voice coil I l, which is mounted to drive the diaphragm l8. Since the details of the loud speaker form, per se, no part of my invention, they are not shown or described in detail.

For the purpose of my invention, it is preferable to insulate the voice coil circuit, comprising the voice coil I1, conductors H and I2 and secondary I, from other parts of the circuit. There may then be provided condenser 8, connected between the anode 5 of the tube I, and either conductor H or l2. From the same conductor to ground there may be provided variable tone control resistor 19. In this instance the speaker field 2|] may be excited through conductor l3, from the same source which provides current for the heater of tube I. The source of sound currents and the speaker may be enclosed in shielding containers l0 and 22, indicated in dotted lines. While I have here illustrated the loud speaker as. of the electro-dynamic type, it will be understood that it may be of the magnetic type and that the term voice coil is intended to apply to the actuating coil of such a speaker as well.

As will be clear from the foregoing, sound voltages to be amplified are impressed between the grid and cathode of the tube, and the amplifled currents are supplied to the winding l of the transformer, and thus impressed on voice coil I1, vibrating it and causing the diaphragm to vibrate, If tone control resistance I9 is set at its maximum value, the shunt circuit around the primary of the output transformer formed by condenser 8, conductor l2, and resistance l9 will be of relatively high impedance to sound currents, and substantially all of the sound currents will pass through the output transformer and thence through the voice coil, producing sounds corresponding thereto. If resistance I9 be lowered, as by'a knob on a rheostat provided for the purpose, then moreor less of the sound currents will be by-passed around the output transformer to ground and will not pass through the voice coil.

The resistance l9 may be continuously variable within the limits desired, or it may be variable in steps and various taps of desired value provided with a tap switch for selecting the desired value. Also, if desired, resistance l9 may be omitted and the tone control action producing by variation of capacity 8, which in this instance may be several condensers which may be of different capacities with a switch having a plurality of contacts for selectively connecting the desired capacity or capacities in circuit as desired. In this case the condenser or condensers used as capacity 8 would be mounted in the speaker mounting, rather than in the receiver chassis.

To provide the simplest form of apparatus, resistance 19 may be omitted and a simple switch be connected in its place, the condenser 8 being preferably in this instance in the receiver chassis.

Since the impedance of condenser 8 is so chosen as to have a substantial selective effect within the audible range, i. e., to have a substantially less impedance to the higher sound frequencies, it will be apparent that the lower the value of resistance IS, the more the high sound frequencies will be by-passed around the voice coil I1, and the higher the value of resistance [9, the more they will pass through the voice coil. Consequently, by adjustment of resistance l9, the tone quality of the reproduction may be 'controlled as desired.

Referring now more particularly to Fig. 2, I have shown the apparatus arranged according to my invention to provide for excitation of the I speaker field winding over the conductors which carry the sound current. In this instance, as before, I represents diagrammatically the final output stage of the amplifier which supplies sound current to the loud speaker l8 through the medium of primary winding 6 and secondary winding 1 and conductors H and 12. In this instance the field coil 20 of the dynamic speaker may be excited from source which may be the same source which excites the filaments of the tubes, through conductor 24, switch 32, to conductor l2. One terminal of the field winding 20 may be connected to the conductor [2 within the speaker chassis as indicated, the other terminal being connected to ground. Under these conditions the voice currents are transmitted over conductors H and I2 as before, and the field excitation current over conductor l2, but the flow of field excitation current along conductor l2 and in the ground return circuit does not interfere with the sound current and there is no harmful effect produced.

Referring now to Fig. 3 I have indicated how radio or audio frequency currents may be passed over the conductor l2 without interfering with the operation of the system. In this instance 29 may indicate a radio or audio frequency source, currents from which are desired to be transferred to the radio or audio frequency load indicated at 28. It will be understood that 28 may be regarded as the radio or audio frequency source and 29 as the load, or that 28 and 29 may be regarded as simply a pair of elements which are desired to be linked together by radio or audio frequency currents, as the case may be.

Oneside of the element 29 may be grounded,

the other side connected to conductor l2 through condenser 26 within the receiver chassis. Similarly conductor l2 may be connected to element 28 through condenser 21 and the opposite side of element 28 grounded. The values of condensers 26 and 21 will be so chosen as to present a low impedance path to the radio or audio frequency current to be utilized in elements 21 and 29, whereby they are substantially pre-' vented from flowing through the transformer winding 1 or voice coil I1.

Referring now to Fig. 4 I have shown still another embodiment of my invention in which the functioning of the receiver may be controlled as by means of a relay by a switch located at or near the loud speaker. In this instance, as before, I represents diagrammatically the final output stage of the amplifier and, in this instance, relay 30 may be connected to ground on one side and on the other to conductor l2. Within the speaker housing conductor l2 may be connected to ground through switch 3| as indicated.

As will be understood, by closure'of the switch 3|, the relay 30 will be energized, current fiowing from source 25, through relay 30, conductor 12, switch 3| to ground and then returning to the source. This relay may be used to control any desired function of the apparatus. For instance, it may operate the on and off switch or, in the case of a radio receiver, it may operate to shift the reception band, or perform other desired functions, as will be understood.

While I have shown and described certain preferred embodiments of my invention, it will be apparent that modifications and changes may be made without departing from the spirit and scope thereof, as will be understood by those skilled in the art.

I claim:

1. In an electrical sound. reproducing system, in combination, means for producing sound'currents, a transformer connected with saidmeans and having primary and secondary windings, a sound reproducer having a voice coil, a pair of conductors connected to said secondary winding and to the terminals of said voice coil for supplying sound currents thereto, and means for controlling the operation of said source from a point adjacent said sound reproducer with only said pair of conductors therebetween, said means comprising a loop circuit having a wire side and a ground return, the wire side being formed by one only of said pair of conductors.

2. In an electrical sound reproducing system, I

in combination, means for producing sound currents, a transformer connected with said means and having primary and secondary windings, a sound reproducer having a voice coil, a pair of conductors for'supplying sound currents from the secondary of said transformer to said voice coil, and a tone control circuit arranged to pass sound currents around said voice coil, said tone control circuit utilizing as a part thereof one only of said conductors.

3. In an electrical sound reproducing system, in combination, means for producing sound currents, a transformer connected with said means and having primary and secondary windings,

a sound reproducer having a voice coil, a closed circuit comprising a pair of conductors extending between said secondary and said voice coil,

and a tone control circuit shunting said voice coil, said tone control circuit comprising, in series, an impedance varying with frequency, a portion of one only of said conductors, and an aperiodic impedance.

4. In an electrical sound reproducing system, in combination, means for producing sound currents, a transformer connected with said means and having primary and secondary windings, a

sound reproducer having a voice coil, a closed circuit comprising a pair of conductors extending between said secondary and said voice coil, and a tone control circuit shunting said voice coil, said tone control circuit comprisingt in series, an impedance varying with frequency, a portion of one only of said conductors and an aperiodic impedance, one of said impedances being variable.

5. In an electrical sound reproducing system, in combination, means for producing sound currents, a transformer connected with said means and having primary and secondary windings, a sound reproducer having a voice coil, 9. closed circuit comprising a pair of conductors extending between said secondary and said voice coil, and a tone control circuit shunting said voice coil, said tone control circuit comprising, in series, an impedance varying with frequency, a portion of one only of said conductors and an aperiodic impedance, said aperiodic impedance being variable.

6. In an electrical sound reproducing system, in combination, means for producing sound currents, a transformer connected with said means and having primary and secondary windings, a sound reproducer having a voice coil, a closed circuit comprising a pair of conductors extending between said secondary and said voicecoil, ancl a tone control circuit shunting said voice coil, said tone control circuit comprising, in series, an

impedance varying with frequency, 'a' portion of one only of said conductors and an aperiodic impedance, said aperiodic impedance being located 'remote from said means for producing soundcurrents.

7. In an electrical sound reproducing system,

in combination, means for producing sound currents, a transformer associated with said means and having primary and secondary windings, a sound reproducer having a moving coil, a pair ,of conductors for' supplying sound currents from the secondary of said transformer to said moving coil, and means'for controlling the operation of said sound current producing means from a point adjacent said sound reproducer without requiring additional conductors extending there- 'between, said means comprising a loop circuit,

one side of which is formed by one of said conductors and the other side by a ground return, a relay for controlling the operation of said sound current producing means, and means at said reproducer for controlling the operation of said relay.

8, In an electrical sound reproducing system, in combination, means for producing sound currents, a transformer connected with said means and having primary and secondary windings, a

sound reproducer having a voice coil, a pair of conductors for supplying sound currents from the secondary of said transformer to said voice coil, a lay-passing circuit around the primary of said transformer, said circuit comprising one only of said pair of conductors and forming a frequency selecting path, at least one condenser in said path mounted within the sound reproducer casing, and means carried by said sound reproducing casing for varying the impedance of said path.

' 9. In an electrical sound reproducing system,

in combination, means for producing sound currents, a transformer connected with said means and having primary and secondary windings, a sound reproducer having a voice coil, apair of conductors connected to said secondary winding and to the terminals of said voice coil for supplying sound currents thereto, and means for controlling the output of said sound reproducer which comprises a loop circuit having a wire side and a ground return, the wire side being formed by one only of said pair of conductors.

HENRY C. FORBES.

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